(TMZ) -- Two more reasons to watch the Super Bowl halftime show -- because, once again, you can BET on whether Lady Gaga will show cleavage ... and the smart money's on "Yes."

TMZ spoke with a rep for BetOnline.ag -- one of the biggest gambling sites on the web -- who told TMZ that they studied hours of tapes to set the odds for this year's prop bet.

The site does the cleavage bet every year -- TMZ was told it's popular with Super Bowl prop bettors. Last year, Beyoncé covered up. The year before that, Katy Perry had a controversial top which resulted in a payout for all bettors.

This year, the odds are in favor of Gaga showing boob:

CLEAVAGE: -$185 (bet $185, win $100)

NO CLEAVAGE: +155 (bet $100, win $155)

Good luck ...

Photo: Getty Images